common raven vs croak

common raven

noun
  • A large all-black passerine bird in the crow family, Corvus corax. 

  • A dark-colored South Asian swallowtail butterfly, Papilio castor 

croak

noun
  • The harsh call of various birds, such as the raven or corncrake, or other creatures. 

  • The call of a frog or toad. (see also ribbit) 

  • A faint, harsh sound made in the throat. 

verb
  • To kill someone or something. 

  • To complain; especially, to grumble; to forebode evil; to utter complaints or forebodings habitually. 

  • To die. 

  • To utter in a low, hoarse voice. 

  • To make a croak. 

  • To make its sound. 

How often have the words common raven and croak occurred in a corpus of books? (source: Google Ngram Viewer )